Pulmonary surfactant is a lipoprotein rich in dipalmitoyl lecithin (DPL) which lines the alveolar-air interface of the lung. Normal surfactant function is essential for adequate respiration and alveolar stability. Little is known about the factors which regulate or modify the secretion of this essential substance onto the lung surface. The aim of this investigation is to elucidate some of the basic characteristics of the secretory process which controls the release of DPL onto the lung surface. I will give rabbits a pulse of radioactive palmitate and will examine the influence of pilo carpine, atropine, iodoacetate and colchicine on the release of DPL into a surface active fraction obtained by lung lavage. I will determine the rate of appearance of radioactive DPL into a surface active fraction of lung lavage in mice, rats, and rabbits to determine if secretion of DPL correlates with respiratory rate and alveolar surface area. I will also determine if the amount of DPL in a surface active fraction of lung lavage returns differ between species. An understanding of the factors which influence the release of surfactant onto the lung surface could lead to better insight into the pathogenesis of the respiratory distress seen in cases of surfactant deficiency or impairment.